This invention relates to control on refrigerating capacity in an air conditioning system using a rotary compressor.
Rotary compressors of sliding vane type can be made to have smaller and simpler structure compared with reciprocating type compressors having intricate structure and the increased number of parts, so that the former has been recently utilized as compressors for use in car coolers. However, some problem has been encountered in the rotary type compressors compared with the reciprocating compressors as follows.
In the case of a compressor for use in the car cooler, a driving force of an engine is transmitted to a pulley of a clutch via a belt so as to drive a rotary shaft of the compressor. Therefore, refrigerating capacity of the compressor of sliding vane type is increased almost linearly in proportion to the number of revolutions of the vehicle engine.
On the other hand, when applying the conventional reciprocating compressor to the car cooler, follow-up capability of an inlet valve is deteriorated while revolving at high speed and compressed gas is not suctioned into a cylinder to the full extent, whereby its refrigerating capacity becomes saturated in high speed operation. More specifically, the reciprocating type compressor is automatically subjected to self-suppressing action on refrigerating capacity while traveling at high speed, while the rotary type compressor is subjected not to such self-suppressing action but the reduction in efficiency or the overcooled state (too much cooling) because of increased compression work thereof. To solve the aforesaid problem in the rotary type compressor, there has been previously proposed a method such that a control valve variable in an opening area of its passage is provided in a passage communicating with the inlet valve of the rotary compressor and the opening area is reduced while revolving at high speeds in order to control capacity of the compressor by utilizing loss of suction. This method, however, has resulted in problems such that the aforesaid control valve has to be provided additionally, structure becomes complicated and manufacturing cost is increased. As an alternative method to avoid excessive capacity of the rotary compressor in high speed operation, there has also been previously proposed such structure as restraining the number of revolutions thereof within a predetermined value by utilizing a fluid clutch, planetary gears or so.
But, for example, the former using the fluid clutch undergoes increased energy loss due to frictional heat generated at the relatively moving surfaces, and the latter using the planetary gears leads to an increase in the number of parts and enlargement of its size. Accordingly, it is difficult to put the foregoing methods into practical use in these days where still more compact and simpler structure is increasingly required in the general trend to energy saving.